Highly conductive composites

ABSTRACT

Domain segregation of polymer blends or block copolymers in the presence of thermal conducting high aspect ratio nanocrystals leads to preferential placement of conductive filler either inside one domain, which promote the self-assembly of a thermal and/or electrical conducting pathway composed of high aspect ratio filler. The self-assembly of such thermal and/or electrical conducting pathway effectively enhances the thermal and/or electrical conductivity of the composite with significantly less amount of filler.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/878,515(allowed), filed Sep. 9, 2010 (published as US 2011-0214284-A1), whichclaims benefit of U.S. Provisional Application No. 61/241,273, filedSep. 10, 2009, the entire contents of each of which are herebyincorporated by reference.

FIELD

The technology herein relates to conductive composite materials, andmore particularly to multi-component domain segregated materials.

BACKGROUND AND SUMMARY Percolation and Nanocomposites

In a conductive network, the conductivity can be guided by percolationtheory. Mathematically, percolation can be described as the following:in an infinite network, there is a path of connected points of infinitelength “through” the network. With increasing population of theconducting points, there exists a critical number above which at leastone conducting pathway forms within the network. The critical point iscalled percolation threshold which is a particle-size andgeometry-dependent parameter for composites. Generally, smallerparticles allow for a lower percolation threshold, due to the fact thataverage particle distance decreases with particle size, given the samevolume ratio, which helps to build the connection pathway of particlesthrough the whole composite. Particle shape is another important factor.It has been shown, both theoretically and experimentally, thatpercolation threshold can be significantly decreased by using highaspect ratio particles.

Previously fillers with different compositions, surface lubrications,and shapes were used for electrically conductive composites, utilizingfillers such as metal beads, metal fibers, metal flakes and metal coatedflakes. Fillers with high aspect ratio were also used in thermallyconductive composites.

Heat transfer in composites is similar to that of electrical conductionexcept that heat is transported by phonons instead of electrons.Nevertheless, similar to electrical conductivity, any given material hasa resistivity against heat flow, therefore, the network rule ofelectrical conductivity applies to thermal conductivity as well.

Applications of Composites

Composites have been and could be applied in several important areas.One area is electronics packaging. Over the past decade, as on chipinterconnect dimensions have been reduced, power to drive the moreresistive circuits has become more and more problematic. New packagingsolutions that do not require liquid cooling are in demand for today'snew chips and circuits. The successful development of compositescontaining high thermal conductivity fillers may ensure that advancedpackaging technology is capable of facing the challenges that may bepresented by current and future generations of chips and circuits.

Another area where composites could be applied is for use as temporarybonding materials for wafer processing. To accommodate the everincreasing demand for smaller IC devices in cell phones, music players,cameras etc, it has become common to grind the fully processed devicewafers to be thinner. After the device wafer is processed on the frontside, it is coated with a temporary bonding adhesive on the front andfurther processed on the back (thinning, etching, metallization, etc.).The device wafer is then detached from the temporary bonding materials.The wafer thinning is often done using aggressive methods that generatea substantial amount of heat, which inevitably raises the wafertemperature, sometimes to as high as 300° C. Better heat dissipation mayreduce the device temperature and/or allow for more aggressive thinningmethods to reduce processing times. Incorporation of thermal conductivefillers could help to increase the thermal conductivity of the temporarybonding materials. Using traditional conductive fillers to effectivelyincrease the thermal conductivity of the composite typically requireshigh levels of loading, which significantly decrease the bondingstrength of the composites. Therefore, it would be useful to develop acomposite with low filler loading and high thermal conductivity forbetter temporary bonding materials.

A third area where composites can be used is for polymers that areelectrically conducting, which can be used in many applicationsincluding conducting pastes or adhesives, charge dissipation materials,transparent conductors, and electromagnetic interference shielding (EMIshielding).

Conducting paste or adhesives are often made by mixing conductive fillerinto adhesive materials and have been widely used in the advancedpackaging industry (such as die attach materials to provide mechanicaladhesion and electrical conductivity between dies and printed circuitboard; or lead-free solder materials to provide electrical interactionbetween devices) in forms of paste, gel or tape. High electricalconductivity often requires high filler loading. Common fillers usedinclude metal flakes, metal fibers, carbon black or carbon fiber.However, adhesion strength and/or mechanical properties often suffer asa result of high filler loading. Therefore, it is desirable to achieveelectrical conductivity using low filler loading.

Transparent conductor materials are required to have a combination ofoptical transparency and electrical conductivity. Their application canbe found in flat panel displays, solar cells, smart windows,photovoltaics, EL lighting and a variety of other optical and electronicapplications, where they can deliver or collect electrons from theactive part of the device while allowing visible photons to pass throughwithout a significant loss. Transparent conductors for commercial scaleneed to be processed easily and cost effectively. Indium Tin Oxide (ITO)is the most widely used transparent conductor due to its superiorcombination of transparency and conductivity. In some applications,fluorine-doped indium oxide (FTO) is used as an alternative to ITO.However, ITO, as well as FTO, is expensive due to the short supply ofindium. Moreover, ITO is far from ideal for many of the fastest growingapplication sectors in which transparent conductors are used. Forinstance, the inherit brittleness of ITO constrains its application intouch screen displays since it cracks easily. Other transparentelectrical conductive film, such as transparent carbon nanotube sheet,while is strong and flexible, is more costly and has not fully enteredindustrial applications.

Electric charges, induced by contact, pressure, or heat, build up on anobject with low electrical conductivity. Rapid discharge of the staticcharge build up can generate a large electric current or an electricalspark, which may be extremely harmful to electronic devices, aroundflammable and ignitable materials, and in space exploration. Increasingthe surface conductivity of the materials helps to reduce the chargebuild up and dissipates static charge to the ground constantly.

Electrically conductive materials are also commonly used for EMIshielding. EMI exists when an electromagnetic disturbance inducesundesirable voltages or currents that adversely influence theperformance of electronics or electrical devices. EMI in radiocommunications has also been called radio frequency interference (RFI).Currently, certain frequency ranges are prohibited or rigorouslyregulated by the government and/or the military. The greatest concernabout EMI besides communications is its effect on electronic devicessuch as onboard sensor systems, pacemakers, electrosurgical units andpersonal computers. Electromagnetic interference works in different waysto degrade the performance of an electronic device. The most common formof interference is the electrical current generated in an electricalcircuit, when it is hit by an electromagnetic disturbance. Dependingupon the magnitude of the electrical disturbance, the induced electricalcurrent can either corrupt a low level signal or override and eventuallydestroy the circuit.

Materials with high electrical conductivity often have high thermalconductivity as well. However, in an application such as anelectric-thermal heating unit, materials with high electricalconductivity and low thermal conductivity are needed. Materials areneeded in the form of bulk, fibers, and films. Some other properties,such as transparency, thermal fatigue tolerance, and toughness need tobe optimized as well.

Example material compositions and processing methods disclosed hereinprovide domain segregation of blends of polymers or polymer and smallmolecule compounds, and/or block copolymers useful to generate athermally and/or electrically conductive pathway composed of thermaland/or electrical conducting fillers.

Composite materials conduct heat and/or electricity through pathwaysconstructed through domain segregation of polymer blends and/or blockcopolymers. The matrix polymers provide mechanical strength to thecomposite and necessary binding properties. They also provideconfinement to the second phase materials, preferably with low meltingpoints or low softening temperatures. Thermal/electrical conductivefillers are purposely and preferentially dispersed in the second phasematerial domains. At the operating temperature, the second phasematerials tend to swell, melt and/or flow and the conductive fillers,such as highly mobile particles can align to form an effectivethermal/electrical conducting pathway.

An example non limiting implementation provides a multi-componentmaterial for thermal conduction, comprising, a first componentcomprising a matrix polymer, a second component comprising a low meltingpoint material immiscible with the first component, and a thirdcomponent comprising a filler material with higher thermal conductivitythan the first and second components. Wherein the third component isdispersed into the second component and the second component isdispersed within the polymer matrix.

An example non limiting implementation provides a process of making amulti-component fluid for use in manufacturing thermally enhancedlayers. This multi-component fluid comprising a polymeric matrixmaterial, a low melting point material and filler particles. The processcomprising capping filler particles with capping agents immiscible withthe polymeric matrix material and miscible in the low melting pointmaterial, dispersing capped filler particles in the low melting pointmaterial and creating a mixture by combining the polymeric matrix andthe low melting point material including the dispersed capped fillerparticles.

An example non limiting implementation provides a product formed by theprocess of making a multi-component fluid. This multi-component fluidcomprising a polymeric matrix material, a low melting point material andfiller particles. The process comprising capping filler particles withcapping agents immiscible with the polymeric matrix material andmiscible in the low melting point material, dispersing capped fillerparticles in the low melting point material and creating a mixture bycombining the polymeric matrix and the low melting point materialincluding the dispersed capped filler particles.

An example non limiting implementation provides a process for assemblinga system having enhanced thermal conductivity. This system comprising anintegrated circuit, a heat sink, and a multi-component compositematerial. The process comprising forming a multi-component compositethermal conductor between the integrated circuit and the heat sink. Themulti-component thermal conductor comprises a matrix material and asecond phase material with high thermal conductive filler material.

An example non limiting implementation provides a multi-componentelectrical conductor with a first component that is a matrix polymer, asecond component that is a low melting point material immiscible withthe first component; and a third component that is a filler materialwith higher electrical conductivity than the first and secondcomponents. The third component is dispersed into the second componentand the second component is dispersed within the polymer matrix. Thethird component provides enhanced electrical conductivity to themulti-component electrical conductor. In addition an examplemulti-component electrical conductor may comprise an opticallytransparent first component and an optically transparent second phasematerial and a third component that is a filler material with higherelectrical conductivity than the first and second components. Therefractive indices of the polymer matrix and the second phase materialmay be similar to each other to minimize internal reflection andmaximize transparency.

One exemplary non-limiting illustrative embodiment provides a compositecomposition made up of multiple components. The multiple componentsystem include, at least two components, preferably three components,and more components in certain applications. This multiple componentsystem includes polymers and fillers to improve the thermal and/orelectrical conductivity of the matrix material in at least onedimension.

One exemplary non-limiting illustrative embodiment provides matrixmaterial that is thermoplastic. Examples include, but are not limitedto, poly(acrylonitrile-butadiene-styrene) (ABS), poly(methylmethacrylate) (PMMA), celluloid, cellulose acetate, poly(ethylene-vinylacetate) (EVA), poly(ethylene vinyl alcohol) (EVOH), fluoroplastics,polyacrylates (Acrylic), polyacrylonitrile (PAN), polyamide (PA orNylon), polyimide-imide (PAT), polyaryletherketone (PAEK), polybutadiene(PBD), polybutylene (PB), polybutylene terephthalate (PBT),polycaprolactone (PCL), polychlorotrifluoroethylene (PCTFE),polyethylene terephthalate (PET), polycyclohexylene dimethyleneterephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs),polyketone (PK), polyester, polyethylene (PE), polyetheretherketone(PEEK), polyetherketoneketone (PEKK), polyetherimide (PEI),polyethersulfone (PES), polyethylenechlorinates (PEC), polyimide (PI),polylactic acid (PLA), polymethylpentenc (PMP), polyphenylenc oxide(PPO), polyphenylcnc sulfide (PPS), polyphthalamide (PPA), polypropylene(PP), polystyrene (PS), polysulfone (PSU), polytrimethylene terephthalate (PTT), polyurethane (PU), polyvinyl acetate (PVA), polyvinylchloride (PVC), polyvinylidene chloride (PVDC),poly(styrene-acrylonitrile) (SAN), etc.

One exemplary non-limiting illustrative embodiment provides matrixmaterial that is a rubber. Examples include, but are not limited to,silicon rubber, fluorinated silicone rubber, natural rubber, vulcanizedrubber, nitrite rubber, styrene butadiene rubber, ethylene propylenediene rubber, neoprene, polyisoprene, polybutadiene, butyl rubber,urethane rubber, hypalon polyethylene, polyacrylate rubber,epichlorohydrin, fluoro carbon rubber, hydrogenate nitrile, etc.

One exemplary non-limiting illustrative embodiment provides matrixmaterial that is thermosetting polymer. Examples include, but are notlimited to, epoxy resin, phenolic resin, unsaturated polyester, melamineresin, urea-formaldehyde, etc.

One exemplary non-limiting illustrative embodiment provides havingsecond phase material being a polymer material with melting point, orsoftening point, or flow point lower than the operating temperature.Examples of a second phase material include, but are not limited to,poly(acrylonitrile-butadiene-styrene) (ABS), poly(methyl methacrylate)(PMMA), celluloid, cellulose acetate, poly(ethylene-vinyl acetate)(EVA), poly(ethylene vinyl alcohol) (EVOH), fluoroplastics,polyacrylates (Acrylic), polyacrylonitrile (PAN), polyamide (PA orNylon), polyamide-imide (PAI), polyaryletherketone (PAEK), polybutadiene(PBD), polybutylene (PB), polybutylene terephthalate (PBT),polycaprolactone (PCL), polychlorotrifluoroethylene (PCTFE),polyethylene terephthalate (PET), polycyclohexylene dimethyleneterephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs),polyketone (PK), polyester, polyethylene (PE), polyetheretherketone(PEEK), polyetherketoneketone (PEKK), polyetherimide (PEI),polyethersulfone (PES), polyethylenechlorinates (PEC), polyimide (PI),polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide(PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene(PP), polystyrene (PS), polysulfone (PSU), polytrimethyleneterephthalate (PTT), polyurethane (PU), polyvinyl acetate (PVA),polyvinyl chloride (PVC), polyvinylidene chloride (PVDC),poly(styrene-acrylonitrile) (SAN), etc.

One exemplary non-limiting illustrative embodiment provides second phasematerial that is a small organic or inorganic molecule or an oligomerwith melting point lower than the operating temperature. Examplesinclude, but are not limited to, paraffin (C₁H_(2n+2)), fatty acids(CH₃(CH₂)_(2n)COOH), alkylamines (CH₃(CH₂)_(2n)NH₂), salt hydrates(M_(n)H₂O), (where M refers to a metal), etc.

One exemplary non-limiting illustrative embodiment provides having thesame material as the polymer matrix and the second phase polymer. Thismultiple component system only has two components with component A beingthe matrix and component C being the conductive filler.

One exemplary non-limiting illustrative embodiment provides fillers withlow aspect ratio. Examples include, but are not limited to, C, Si, Ge,Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy, Gd, CuCl, CuBr, CuI,AgCl, AgBr, AgI, Ag₂S, Al₂O₃, Ga₂O₃, In₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂,MgO, Eu₂O₃, CrO₂, CaO, MgO, ZnO, Mg_(x)Zn_(1-x)O, SiO₂, Cu₂O, Zr₂O₃,ZrO₂, SnO₂, ZnS, HgS, Fe₂S, Cu₂S, CuIn₂S₂, MoS₂, In₂S₃, Bi₂S₃, GaP,GaAs, GaSb, InP, InAs, In_(x)Ga_(1-x)As, SiC, CaF₂, YF₃, YSi₂, GaInP₂,Cd₃P₂, CuIn₂Se₂, In₂Se₃, HgI₂, PbI₂, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,BN, AlN, GaN, InN, Si₃N₄, ZrN, Y₂O₃, HfO₂, Sc₂O₃, etc.

One exemplary non-limiting illustrative embodiment provides fillers withhigh aspect ratio. Examples include, but are not limited to, C, Si, Ge,Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy, Gd, CuCl, CuBr, CuI,AgCl, AgBr, AgI, Ag₂S, Al₂O₃, Ga₂O₃, In₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂,MgO, Eu₂O₃, CrO₂, CaO, MgO, ZnO, Mg_(x)Zn_(1-x)O, SiO₂, Cu₂O, Zr₂O₃,ZrO₂, SnO₂, ZnS, HgS, Fe₂S, Cu₂S, CuIn₂S₂, MoS₂, In₂S₃, Bi₂S₃, GaP GaAs,GaSb, InP, InAs, In_(x)Ga_(1-x)As, SiC, CaF₂, YF₃, YSi₂, GaInP₂, Cd₃P₂,CuIn₂Se₂, In₂Se₃, HgI₂, PbI₂, ZnSe, CdS, CdSe, CdTe, HgTe, PbS, BN, AlN,GaN, InN, Al_(x)Ga_(1-x)N, Si₃N₄, ZrN, Y₂O₃, HfO₂, Sc₂O₃, layeredsilicate clays, talc, layered perovskites, etc.

Another exemplary non-limiting illustrative embodiment provides amultiple component composite system with two polymers and two fillers.The second filler can either be a conductive filler to further enhancethe thermal and/or electrical conductivity of the composite ormechanical reinforcing filler which provides extra physical strength tothe composites. Example of the second filler include, but are notlimited to, alkyltrimethylsilane capped silica colloids preferentiallyentering the matrix material (component A) as thermally conductivefiller, alkylphosphoric acid capped carbon nanotubes preferentiallyentering the matrix material (component A) as thermal and/or electricalconductive filler and mechanical reinforcing filler.

One exemplary non-limiting illustrative embodiment provides methods forapplying the composite. The methods include, but are not limited to,curing, polymerization, laminating, extrusion, injection molding, moldcasting, spin coating, dip coating, brushing, spraying, printing, etc.

One exemplary non-limiting illustrative embodiment provides having ahigh aspect ratio filler chemically bonded with the low melting pointpolymer that is in-situ polymerized. The chemical bonds promote thealignment of the high aspect ratio fillers as the low melting pointpolymer melt and flow at the working temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better and morecompletely understood by referring to the following detailed descriptionof non-limiting example illustrative embodiments in conjunction with thedrawings, of which:

FIG. 1 a shows an exemplary illustrative non-limiting multiple componentcomposite material.

FIG. 1 b is a close up of an exemplary multiple component materialshowing the phase segregated materials and fillers in one phase.

FIG. 2 a shows an exemplary illustrative non-limiting multiple componentcomposite material.

FIG. 2 b is a close up of an exemplary multiple component materialshowing the phase segregated block co-polymers and fillers in one of thephases.

FIG. 3 is a flow chart showing an exemplary illustrative non-limitingprocess flow to prepare a multiple component composite

FIG. 4 shows an exemplary non-limiting example thermal interfacecomposite film sandwiched between die and heatsink.

FIG. 5 shows an exemplary non-limiting example temporary bondingmaterial sandwiched between IC chip and positioning chuck and a grinder.

FIG. 6 shows an exemplary non-limiting example charge dissipatingcomposite material coated on a substrate of electronic devices. Thecharge dissipating material is grounded with a wire(s).

FIG. 7 shows an exemplary non-limiting example electromagneticinterference (EMI) shielding material coated on a substrate ofelectronic devices.

FIG. 8 shows an exemplary non-limiting example electrical-thermalheating film coated on glass and is connected to electrical power supplyby wires from the edges.

FIG. 9 shows an exemplary non-limiting example underfill materialsandwiched between an IC chip and the underlying circuit boardsubstrate.

DETAILED DESCRIPTION OF NON-LIMITING ILLUSTRATIVE EMBODIMENTS MultipleComponent System

One exemplary non-limiting illustrative embodiment provides a two phasepolymer material with at least one type, shape or phase of filler in atleast one polymer phase. One phase of polymer is the matrix material(Component A) and the other phase of the polymer is a low meltingmaterial (Component B) or low softening temperature material. The matrixmaterial can be either a thermosetting polymer, or a thermoplasticpolymer, or a rubbery material which provides the required mechanicalproperties and necessary binding properties of the composites. Thesegregated second phase material could be, but not limited to, apolymeric material with relatively low melting point depending on thedesired working temperature (melting point lower than the workingtemperature). This segregated domain flows above its melting temperatureto fill up any air gaps at the interface between the composite and thesubstrate to ensure the maximum contact area. The filler (Component C)can be micro-sized particles, or preferably sub-micron sized particlesor more preferably nanoparticles, or even more preferably high aspectratio nanoparticles.

An exemplary composite film (101) is shown in FIG. 1 a. A polymer blendmade with two immiscible materials (102 and 103) can phase segregateinto micron or submicron sized domains. One phase of the blend can be apolymer matrix material (102) and the other phase can be a low meltingpoint material (103). High aspect ratio fillers (104) can be placed inthe low melting point phase. They may only be present in this phase. Anddue to geometrical confinement effect (the length of particles may bebigger than the width of the domain), the particles may bepreferentially aligned. FIG. 1 b shows the blow up of the region wherethe first phase (102) and the second phase (103) materials aresegregated and the fillers (104) are in the second phase material.

One exemplary non-limiting illustrative embodiment provides that thefillers selectively enter into the low melting point polymer domain bychoosing appropriate surface passivation agents. This effectivelyreduces the percolation threshold of the composite since percolation isonly needed in the domains instead of in the whole composite, since thesecond phase domain is populated enough to form percolation for thewhole composite.

One exemplary non-limiting illustrative embodiment provides animmiscible polymer blend with segregated domain size in the rangebetween several hundred nanometers and several micrometers. Themorphology and the size of the domains are controlled by the compositionof the polymers, the physical properties of the polymers and theprocessing condition of the blend.

The various components of the composites serve different purposes.Component A, or the polymer matrix, accounts for majority of the volumeof the composite, preferably 50-65%. The polymer matrix can be athermoset, a thermoplastic or a rubber. It binds the composite to theheat generating electronic components (die) on one side and the heatdissipating block (heatsink) on the other side as illustrated in FIGS. 1and 2. Component A, as the dominant component in the composites,contributes the most to the physical properties of the composite.Component A may yield the worst conductivity by itself, if it is notfilled with conductive fillers. One example of thermoset matrix polymeris epoxy, one example of thermalplastic matrix polymer is polyimide, andone example of rubber matrix polymer is silicon rubber, which havethermal conductivities of approximately 0.18 W/m·K, 0.52 W/m·K, and 0.22W/m·K, respectively.

Component B can be a polymer material that has a low melting point orlow softening temperature. It may account for less than 50% of thevolume of the composites, preferably 10-45%, more preferably 15-35%. Ittends to swell, soften, and/or melt upon heating at the operatingtemperature. One advantage of using low melting point or low softeningpoint materials as the second phase is to eliminate any air gap betweenthe composite and the substrates (die and heatsink), while the matrixpolymer may not be able to undergo any further major physicaldeformation to conform to the rough substrate. A melted or softenedsecond phase may also facilitate the motion of the filler so that theycan easily align along the preferred direction.

One exemplary non-limiting illustrative embodiment provides examples oflow melting point polymers with adjustable melting points. Theseexamples include, but are not limited to, polyethylene oxide (PEO) andpoly(ε-caprolacton) (PCL). Polyethylene oxide with molecular weightlower than 20,000 is commonly referred to as polyethylene glycol (PEG).The melting point of PEO is around 70° C. Reducing the molecular weightof PEO and turning it into oligomers can drop the melting point to belowroom temperature. Therefore, by choosing the molecular weight of the PEOor oligo-PEG, the operating temperature of the composites can be variedto span temperature range from room temperature to 70° C. For otheroperating temperature, polymers with appropriate melting points can bechosen accordingly. The choice of melting point or softening pointdefines the operation temperature of the composite. Furthermore,Component B can also be chosen from a series of low melting pointnon-polymeric materials (such as stearic acid) or oligomer materials.

Another exemplary composite material (201) is shown in FIG. 2 a. Apolymer matrix material (202) and a second phase material (203) can bechemically bonded to each other as a block co-polymer. One chain segmentof the block co-polymer can have a lower melting point than the otherchain segment. The segment of the block co-polymer with a lower meltingpoint can be the second phase material (203). The block co-polymer canself assemble into a two phase system and the low melting point phasecan be segregated into micron or submicron sized domains. These micronor submicron size domains can be aligned in the desired direction. Thedomain size of block copolymer can be in the range between 10 to 50 nm.High aspect ratio fillers (204) can enter into the low melting pointphase and due to geometrical confinement effect (the length of particlesmay be bigger than the width of the domain) they align in the samedirection as the domains of the second phase. FIG. 2 b shows the blow upof the region where the first phase (202) and the second phase (203)materials of the block co-polymer are segregated and the fillers (204)are in the second phase (203) material.

Another exemplary non-limiting illustrative embodiment provides having apolymer matrix and a second phase polymer chemically bonded to eachother as a block copolymer. Examples of block copolymers include, butare not limited to, polymethylmethyacrylate-b-polyethylene oxide(PMMA-b-PEO), polystyrene-b-ethylene oxide (PS-b-PEO), poly(dimethylsiloxane-b-adipic anhydride) (PDMS-b-PAA), poly(methylmethacrylate-b-vinyl pyridine) (PMMA-b-PVP), Poly(vinylnaphthalene-b-t-butyl acrylate) (PVN-b-PBA),polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL), etc. Morepreferably, the matrix can be a block copolymer with one block being thehigh temperature resistant polymer and the second block being the lowmelting point polymer. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

Component C is a microsized or nanosized and preferably high aspectratio conductive filler. The filler has a high thermal and/or electricalconductivity. It only accounts for 1-49%, preferably 2-15% of the volumeof the composite. Low filler loading assures the minimum impact offiller on the morphology of the domain segregation of the polymer blendor block copolymer. More importantly, the low filler loading cansubstantially decrease the degradation of the adhesion property of thematerials by large filler loading that is otherwise used to provide thedesired higher conductivity. As discussed in the background, high aspectratio filler lowers the percolation threshold of the composite. Inanother word, less filler may be needed to provide a conducting pathwaythrough the composite. By making the fillers incompatible with thematrix polymer and compatible with the low melting pointpolymer/oligomer, fillers enter into the low melting pointpolymer/oligomer phase only and lower the percolation threshold evenmore as illustrated in FIG. 1 and FIG. 2. This may be accomplished bychoosing the passivating agents on the fillers such that they arecompatible with the low melting point polymer/oligomer phase. Oneexample of the conductive filler is silver nanowires that can besynthesized in large quantities with a diameter of 50 nm and the lengthof 8 μm. The surface of the nanowires can be passivated withPolyvinylpyrrolidone (PVP). Subsequent surface modification with thiolterminated polyethylene oxide provides the compatibility of thenanowires when the second phase, i.e. low melting point polymer phase,is chosen to be polyethylene oxide.

The selection of the dimension of the filler needs to be based on thedomain size and domain morphology of the polymer blends and blockcopolymers. In most of the situations, cylindrical shape with highaspect ratio (the ratio of length/diameter) may be preferable. Highaspect ratio significantly reduces the critical concentration needed toform a conduction pathway in the composite. The diameter of the fillersneeds to be very small compared with the domain size so that thepresence of the filler does not significantly interfere with the domainsegregation behavior. The length of the filler should to be similar tothe domain size on the lateral direction to maximize the geometricalconfinement effect. With filler length approaching the domain size, thelong axis of the filler may preferentially align with the long axis ofthe polymer domain. As a result, the fillers align along the heattransfer direction as illustrated in FIG. 1 and FIG. 2, which furtherreduces the percolation threshold.

The fillers are placed preferentially into the low melting point phasebecause the alignment of the filler can proceed much easier in a meltedor softened material phase with reduced viscosity. The flow of moltenpolymer to conform to the substrate may also bring the heat conductingfillers to the interface to provide heat and/or electrical conductiondirectly toward the substrate.

Another exemplary non-limiting illustrative embodiment provides acomposite system with a ceramic matrix material. One example includesfilling anodized porous Al₂O₃ (matrix material), which has straightchannels with diameter between 20 nm and 500 nm, with polystyrene as thesecond phase. Polystyrene has a melting point of 240° C. And the fillercan be polystyrene capped MN nanorods.

Example Non-Limiting Processing and Fabrication Methods

Each component of the composite can be homogenized, using differentmethods, before they can be made into a composite material suitable fordifferent applications with desired morphology. Fillers are generallycompatible with the phase which they preferentially enter.

One exemplary non-limiting illustrative embodiment provides a method ofproviding dispersability of fillers in composites. Fillers can be cappedwith surfactant molecules or functionalized polymers for this purpose.Examples of the surfactant molecules include, but are not limited to,alkylsilanes, alkylthiols, alkylamines, alkylcarboxylic acids,alkylphosphoric acids, alkylphosphine oxides, alkylphosphines,alkylammonium salts, etc. Examples of the functionalized polymersinclude, but are not limited to, polyols, polyacrylic acids, polyacrylicamines, thiol-terminated polymers, silane-terminated polymers,amine-terminated polymers, carboxylic acid-terminated polymers, etc. Thesurfactant molecules or the functionalized polymers can be compatiblewith the second phase material. Examples include, but are not limitedto, thiol-terminated poly(ε-caprolactone) when poly(ε-caprolactone) isused as second phase material, etc.

One exemplary non-limiting illustrative embodiment provides a method tohomogenize the composite. The capped filler is first mixed with meltedsecond phase material. The homogeneous mixture of filler with the secondphase material is then mixed with the matrix material. The mixingmethods include, but are not limited to, stirring, high shear blending,extruding, homogenizing, ball-milling, sonication, three-roll-milling,in-situ polymerization, solvent blending, etc.

One exemplary non-limiting illustrative embodiment provides a method ofproviding dispersability of fillers in composites. Fillers can be firstmixed or chemically bonded with the monomer of the second phasepolymers, followed by in-situ polymerization of the second phasepolymer. The formed filler/second phase polymer composite is then mixedwith the matrix material. The mixing methods include, but are notlimited to, stirring, high shear blending, extruding, homogenizing,ball-milling, sonication, three-roll-milling, in-situ polymerization,solvent blending, etc.

After the composite is homogenized, it can be made into a form suitablefor different applications.

Another exemplary non-limiting illustrative embodiment provides a methodfor forming a film from a multiple component system wherein the meltingpoint of the second phase material starts out higher than the meltingpoint of the matrix material. Fillers are first dispersed in the secondphase material by solvent blending, followed by the formation of microsize spheres or ovals of the filler/second phase material composite.These spheres or ovals can be covered with a shell of the matrixmaterial. The mixture is applied to a surface and heated above themelting point of the matrix material but below the melting point of thesecond phase material in order to maintain the integrity of the secondphase. The matrix material melts and flows from the surface of fillerloaded second phase material and forms the matrix. Then the chemicalstructure of the matrix material can be modified to increase its meltingpoint. For example UV light can be applied to the film to crosslink thematrix material and increase the melting point above the melting pointof the second phase material. This method provides an innovative routeto obtaining the desired second phase domain structure within the matrixmaterial.

FIG. 3 shows an exemplary process flow for preparing a multiplecomponent composite. The process starts with the synthesis of fillerparticles. The filler particle can then be capped with desired cappingagents to provide compatibility between filler particles and low meltingpoint second phase material. Following that, the capped filler particleis blended with the low melting point second phase materials and themixture is then mixed with matrix material and homogenized. The formingof the composite can be achieved in several processes. One exemplaryprocess may be to heat the composite mixture and extrude it into itsfinal form. Another exemplary process may be to heat the compositemixture and inject mold it into its final form. One other exemplaryprocess may be to heat the composite mixture and compression mold, resintransfer mold or laminate the composite into its final form. The otherexemplary process may be to coat a surface with the composite mixture bydipping, spinning, spraying, brushing, sputtering, painting, orprinting. The coating is then heated into its final form.

Example Non-Limiting Filler Alignment Methods (Methods to InduceAlignment of Fillers at Desired Direction)

Aligning the conductive fillers, preferentially high aspect ratiofillers, significantly decrease the percolation threshold. As a result,the effective filler loading needed to achieve desired conductivity isdecreased.

One exemplary non-limiting illustrative embodiment provides having ahigh aspect ratio filler in the low melting point polymer domain. Themicro and nano-sized domains promote alignment of the high aspect ratiofillers along the heat conducting direction due to geometricalconfinement effect. Preferably, the longer dimension of the high aspectratio filler is similar to the longer dimension of the conductingpathway formed by the low melting point polymer domain. The longerdimension of the high aspect ratio filler can be longer than the shorterdimension of the conducting pathway formed by the low melting pointpolymer.

Another exemplary non-limiting illustrative embodiment provides themechanism to align the fillers along designed conducting direction underthe influence of an external field. Conductive filler can respond to anexternal electrical and/or magnetic field. When the second domain ismobile, either during processing or during operating, the high aspectratio filler can be aligned in desired direction by applying anelectrical field or magnetic field along the conduction direction.

One exemplary non-limiting illustrative embodiment provides a mechanismto fix the alignment of the high aspect ratio filler. During compositeprocessing period, both the matrix material and second phase materialare mobile. High aspect ratio filler may be aligned during the processunder geometrical confinement, induced by, thermal gradients, electricalfields, or magnetic fields. One example provides the alignment prior tothe material being put into operation. Alignment of the high aspectratio filler is induced during the processing of the material. After thecomposite is formed, the domain structure can be permanently preservedby reducing the temperature and freezing the second phase.

Example Non-Limiting Application as Thermal Interface Materials

FIG. 4 shows an exemplary thermal interface composite material (401)sandwiched between die (402) and heat sink (403). The thermal interfacecomposite material may be similar to the composite material described inFIG. 1 or FIG. 2. The fillers may align in the direction of heat flowfrom the die to the heat sink. Thermal interface materials (TIMs) serveas a heat conducting interface between an IC chip and the heat sink. Itnot only dissipates the excessive amount of heat generated by IC chipstoward the heat sink, but also provides mechanical bonding between theIC chips and the heat sink. Traditional TIMs often suffer from lowadhesion, low toughness, low tolerance to thermal fatigue and surfaceroughness, and high hardness due to the high filler loading required toobtain desired thermal conductance. A thermal interface compositematerial can deliver enhanced thermal conductance with small fillerloading. Furthermore, the multi-component thermal interface compositematerials can have a reduced coefficient of thermal expansion (CTE)compared to the matrix and the second phase materials. By theincorporation of rigid fillers the CTE of the composite material can bematched to the CTE of the silicon chips. Thermal expansion mismatchtypically cause residue stress and thermal fatigue which cansignificantly decrease the thermal cycling life of the devices.

One exemplary non-limiting illustrative embodiment provides using amultiple component system for thermal management in electronic devicesas thermal interface material (TIM). Preferably, a three componentsystem can be used, with component A being at least one thermoset,thermoplastic, or rubber polymer, with component B being at least onelow melting point polymer, and with component C being at least one typeof conductive filler and conductive filler selectively enteringcomponent B. Even more preferably, a four component system can be used,with component A being at least one thermoset, thermoplastic, or rubberpolymer, with component B being at least one low melting point polymer,with component C being at least one type of conductive filler thatselectively enters into component B, and with component D being the sameor different type of conductive filler.

An advantage of example non-limiting embodiments herein compared withtraditional thermal interface materials (TIMs) is the utilization ofsignificantly reduced filler loading. Traditionally TIMs often sufferfrom low adhesion strength, low toughness, low tolerance to thermalfatigue and surface roughness, and high hardness. A three (or more)component system reduces the above mentioned problems by reduced fillerloading. Other advantages may include, but are not limited to, highoptical transparency, improved processability, improved thermal fatiguetolerance, and improved mechanical fatigue tolerance.

One exemplary non-limiting illustrative embodiment provides athermoplastic matrix material for TIM application. The thermoplastic isheat resistant with a softening temperature higher than the operatingtemperature. Examples include, but are not limited to,poly(acrylonitrile-butadiene-styrene) (ABS), fluoroplastics, polyamide(PA or Nylon), polyamide-imide (PAI), polyetheretherketone (PEEK),polyurethane (PU), polyvinyl chloride (PVC), etc.

One exemplary non-limiting illustrative embodiment provides a rubbermatrix material for TIM application. The rubber is heat resistant withsoftening temperature higher than the operating temperature. Examplesinclude, but are not limited to, silicon rubber, fluorinated siliconerubber, vulcanized rubber, fluoro-carbon rubber, etc.

One exemplary non-limiting illustrative embodiment provides thermosetmatrix material for TIM application. More preferably, the thermoset isheat resistant with softening temperature higher than the operatingtemperature. Examples include, but are not limited to, epoxy resin,phenolic resin, urea-formaldehyde, etc.

One exemplary non-limiting illustrative embodiment provides having asecond phase material in the matrix material for TIM application. Morepreferably, the second phase material is immiscible with the matrixmaterial. Example systems include, but are not limited to, polyethyleneoxide for epoxy resin matrix, poly(E-carprolactone) for silicon rubber,etc.

One exemplary non-limiting illustrative embodiment provides a blockcopolymer matrix material for TIM application. More preferably, thematrix can be a block copolymer with one block being the hightemperature resistant polymer and the second block being the low meltingpoint polymer. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),Poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

One exemplary non-limiting illustrative embodiment provides fillers withlow aspect ratio for TIM application. More preferably, fillers with highthermal conductivity can be used. Examples include, but are not limitedto, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy, Gd, ZnO, SiO₂,BN, AlN, GaN, Al_(x)Ga_(1-x)N, Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂, MgO, EuO,CrO₂, Y₂O₃, HfO₂, etc.

One exemplary non-limiting illustrative embodiment provides fillers withhigh aspect ratio for TIM application. More preferably, fillers withhigh thermal conductivity can be used. Examples include, but are notlimited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy, Gd, ZnO,SiO₂, BN, AlN, GaN, Al_(x)Ga_(1-x)N, Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂,MgO, EuO, CrO₂, Y₂O₃, HfO₂, layered silicate clays, talc, layeredperovskites, etc.

Thermally conductive fillers can be capped and mixed into low meltingpoint phase, then is blended with the matrix polymer. One exemplarynon-limiting illustrative embodiment provides that ZnO nanorods that arepassivated with silane terminated polyethylene oxide. The ZnO nanorodsare stirred into polyethylene oxide at temperature above a suitabletemperature (e.g. 80° C. or some other suitable temperature) until atransparent mixture is achieved. Epoxy resin is then added to thissolution and stirred at a suitable temperature (e.g. 80° C.) to obtain ahomogeneous mixture. Curing agent is finally added and stirred at asuitable temperature (e.g. 80° C.) to make the composite material.

The composite is then formed between die and heat sink. One exemplarynon-limiting illustrative embodiment provides that the homogenouscomposite mixture is applied onto the bottom of the heat sink, and theheat sink is pasted onto the die. The device is then cured at a suitabletemperature (e.g. 140° C.) for a suitable time (e.g. 8 hr). Anotherexemplary non-limiting illustrative embodiment provides that thehomogenous composite mixture is applied onto the die, and the die ispasted onto the heat sink. The device is then cured.

Example Non-Limiting Application as Temporary Bonding Materials forWafer Processing

FIG. 5 shows an exemplary non-limiting multi-component compositematerial as a temporary bonding material (501). Exemplary temporarybonding material (501) is sandwiched between an IC chip (502) and apositioning chuck (503). The backside of the IC chip (502) can then beground by a polisher (504). This temporary bonding composite materialmay be similar to the composite material described in FIG. 1 or FIG. 2.The fillers may align in the direction of heat flow from the IC chiptowards the positioning chuck. Temporary wafer bonding materials provideadhesion between the positioning chuck and the front face of a fullyprocessed IC chip. Then the IC chip can be thinned from the back sidemechanically. Due to the excessive heat generated by the aggressivegrinding process, the IC chip often heats up to as high as 300° C. Thetemporary bonding materials not only sustain the high operatingtemperature, they are also ideal materials to provide enhanced heatconductance for effective cooling of the chip. A multi-componentcomposite temporary bonding material can provide the heat conductivitywithout sacrificing the bonding strength. The glass transitiontemperature of the polymers can also be favorably increased to allow forhigher operating temperature.

One exemplary non-limiting illustrative embodiment provides using amultiple component composite system as temporary bonding materials forwater processing. Preferably, a two component system can be used, withcomponent A being at least one of thermoset, thermoplastic, or rubberpolymer, and with component C being at least one type of thermallyconductive filler. More preferably, three component system can be used,with component A being one of thermoset, thermoplastic, or rubberpolymer, with component B being a low melting point polymer or oligomer,and with component C being a thermally conductive filler thatselectively enters into component B. Even more preferably, fourcomponent system can be used, with component A being one of thermoset,thermoplastic, or rubber polymer, with component B being a low meltingpoint polymer or oligomer, with component C being a thermally conductivefiller that selectively enters into component B, and with component Dbeing the same or different type of conductive filler that selectivelyenters into component A.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system comprising at least one matrix polymer,to be used as temporary bonding materials for water processing. Matrixmaterial may be a thermoplastic, or thermoset, or rubber polymer. Morepreferably, the matrix material is capable of providing high bondingstrength, and high thermal fatigue tolerance. Examples of matrixmaterials include, but are not limited to, silicone rubber, epoxy resin,phenolic resin, polyimide, unsaturated polyester, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one second polymer, to beused as temporary bonding materials for water processing. Preferably thesecond polymer has a lower melting point than the operation temperatureof the wafer processing. More preferably, the second polymer isimmiscible with the matrix material. Examples of a multiple componentsystem include, but are not limited to, polyethylene oxide for epoxyresin matrix, poly(ε-carprolactone) for silicon rubber matrix, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one block copolymer asthe matrix polymer, to be used as temporary bonding materials for waferprocessing. More preferably, the matrix can be a block copolymer withone block being the high temperature resistant polymer and the secondblock being the low melting point polymer. Examples of block copolymersinclude, but are not limited to, polydimethylsiloxane-b-ethylene oxide(PDMS-b-PEO), poly(dimethylsiloxane-b-E-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane), etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler material withlow aspect ratio, to be used as temporary bonding materials for waterprocessing. Preferably fillers enter into the second polymer phase. Morepreferably, fillers with high thermal conductivity can be used. Examplesof fillers include, but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd,Fe, Pb, Al, Zn, Co, Dy, Gd, ZnO, SiO₂, BN, AlN, GaN, Al_(x)Ga_(1-x)N,Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂, MgO, EuO, CrO₂, Y₂O₃, HfO₂, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler material withhigh aspect ratio, to be used as temporary bonding materials for waterprocessing. Preferably filler enters into the second polymer phase. Morepreferably, fillers with high thermal conductivity can be used. Examplesof fillers include, but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd,Fe, Pb, Al, Zn, Co, Dy, Gd, ZnO, SiO₂, BN, AlN, GaN, Al_(x)Ga_(1-x)N,Al₂O₃, FeO, Fe₂O₃, Fe₃O₄, TiO₂, MgO, EuO, CrO₂, Y₂O₃, HfO₂, layeredsilicate clays, talc, layered perovskites, etc.

Example Non-Limiting Applications as Electrical Conductor

FIG. 6 shows an exemplary non-limiting charge dissipating compositematerial (601) coated on the electronic device (602). The chargedissipating material is grounded with a wire(s) (603). This chargedissipating composite material may be similar to the composite materialdescribed in FIG. 1 or FIG. 2. The fillers may align in the directionparallel to the substrate to maximize the electron conduction toward thegrounding wire.

One exemplary non-limiting illustrative embodiment provides theapplication of electrical conductive composites as conducting paste oradhesive to provide electrical interaction between devices, or betweendie and printed circuit-board.

One exemplary non-limiting illustrative embodiment provides theapplication of electrically conductive composites as charge dissipatingcoating layer. Electrostatic charge builds up on surfaces of electronicdevices. Without proper grounding, occasional discharge may happenleading to electrical sparks or unwanted high surface current, whichdamages the devices. Coating the substrate with electrically conductivematerials, as illustrated in FIG. 6, can serve as a charge dissipatinglayer when they are properly grounded.

FIG. 7 shows an exemplary non-limiting electromagnetic interference(EMI) shielding composite material (701) coated on the electronic device(702). This electromagnetic interference (EMI) shielding compositematerial may be similar to the composite material described in FIG. 1 orFIG. 2.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system to be applied as an EMI shielding material toabsorb or reflect unwanted electromagnetic signals to prevent them fromentering or leaving the IC devices as illustrated in FIG. 7.

One exemplary non-limiting illustrative embodiment provides using amultiple component composite system as an electrical conductor.Preferably, a three component system can be used, with component A beingat least one of thermoset, thermoplastic, or rubber polymer, withcomponent B being a low melting point polymer, and with component Cbeing at least one type of conductive filler that selectively entersinto component B. Even more preferably, a four component system can beused, with component A being at least one of thermoset, thermoplastic,or rubber polymer, with component B being a low melting point polymer,with component C being at least one type of electrically conductivefiller that selectively enters into component B, and with component Dbeing the same or different type of electrically conductive filler thatselectively enters into component A.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one matrix material thatis one of thermoplastic, or thermoset or rubber material, for use as anelectrical conductor. More preferably, the matrix material is capable ofproviding mechanical properties and physical properties that can betailored to match the needs of a variety of different applications.Examples of matrix materials include, but are not limited to, siliconerubber, epoxy resin, phenolic resin, polyimide, unsaturated polyester,etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one second phase polymermaterial, for use as an electrical conductor. More preferably, thesecond phase polymer is immiscible with the matrix material. Examples ofsecond phase polymers include, but are not limited to, polyethyleneoxide for epoxy resin matrix, poly(E-carprolactone) for silicon rubber,etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one block copolymermatrix material, for use as an electrical conductor. More preferably,the matrix can be a block copolymer with one block being the low meltingpoint polymer. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),Poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with lowaspect ratio, for use as an electrical conductor. Preferably, fillerenters into the second phase material. More preferably, fillers withhigh electrical conductivity can be used. Examples of fillers include,but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co,Dy, Gd, etc. Even more preferably, nanoparticle can be used. Example ofnanoparticles include, but are not limited to, carbon blacknanoparticles, C60 fullerene, gold nanoparticles, silver nanoparticles,etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system with at least one filler with highaspect ratio, for use as an electrical conductor. Preferably, fillerenters into the second phase material. More preferably, fillers withhigh electrical conductivity can be used. Examples of fillers include,but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co,Dy, Gd, etc. Even more preferably, nanowires and nanorods can be used.Examples include, but are not limited to carbon nanotubes, silvernanowires, gold nanorods, etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system with at least one filler with highaspect ratio, for use as an electrical conductor. Preferably, fillerenters into the matrix material.

Example Non-Limiting Application as Transparent Conductor Materials

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system as a transparent conductor material. In thisapplication, transparent polymers can be chosen as the matrix materialand the second phase material can be chosen to have a matchingrefractive index with the matrix material to minimize opticalscattering. An exemplary non-limiting illustrative embodiment providesthe use of low filler loading to achieve desired electricalconductivity, while maintaining the optical transparency, especiallywhen nano-sized fillers are used.

One exemplary non-limiting illustrative embodiment provides using amultiple component composite system as an electrical conductor.Preferably, a three component system can be used, with component A beingat least one of thermoset, thermoplastic, or rubber polymer, withcomponent B being a low melting point polymer, and with component Cbeing at least one type of conductive filler that selectively entersinto component B. Even more preferably, a four component system can beused, with component A being at least one of thermoset, thermoplastic,or rubber polymer, with component B being a low melting point polymer,with component C being at least one type of electrically conductivefiller that selectively enters into component B, and with component Dbeing the same or different type of electrically conductive filler thatselectively enters into component A.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one transparent matrixmaterial that is one of thermoplastic, or thermoset or rubber material,for use as a transparent conductor material. More preferably, the matrixmaterial is capable of providing mechanical properties and physicalproperties that can be tailored to match the needs of a variety ofdifferent applications and has high optical transparency at desiredwavelength range. Examples of matrix materials include, but are notlimited to, methacrylate polymers, polycarbonate, cyclic olefinpolymers, styrenic polymers, fluorine-containing polymers, polyesters,polyethersulfone, polyimides, silicone rubber, epoxy resin, phenolicresin, unsaturated polyester, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one second phase polymermaterial, for use as transparent conductor materials. More preferably,the second phase polymer is immiscible with the matrix material. Evenmore preferably, the second phase polymer has a refractive indexmatching the refractive index of matrix materials (component A).Examples of second phase polymers include, but are not limited to,poly(N-vinyl pyrrolidone) (refractive index 1.53) for epoxy resin matrix(refractive index 1.55); poly(vinyl alcohol) (refractive index 1.50) forpolymethyl methacrylate (refractive index 1.49), etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one block copolymermatrix material, for use as a charge dissipating material. Morepreferably, the matrix can be a block copolymer with one block being thelow melting point polymer. Small domain size (sub 100 nm) improves theoptical transparency. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),Poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with lowaspect ratio, for use as a transparent conductor material. Preferably,filler enters into the second phase material. More preferably, fillerswith high electrical conductivity can be used. Examples of fillersinclude, but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al,Zn, Co, Dy, Gd, etc. Even more preferably, nanoparticle can be used.Example of nanoparticles include, but are not limited to, carbon blacknanoparticles, C60 fullerene, gold nanoparticles, silver nanoparticles,etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system with at least one filler with highaspect ratio, for use as a electrical conductor. Preferably, fillerenters into the second phase material. More preferably, fillers withhigh electrical conductivity can be used. Examples of fillers include,but are not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co,Dy, Gd, etc. Even more preferably, nanowires and nanorods can be used.Examples include, but are not limited to carbon nanotubes, silvernanowires, gold nanorods, etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system with at least one filler with highaspect ratio, for use as a transparent conductor material. Preferably,filler enters into the matrix material.

Example Non-Limiting Application as Electrical-Thermal Heating Materials

FIG. 8 shows an exemplary non-limiting electrical-thermal heatingmaterial (801) coated on glass (802) and is connected to electricalpower supply (803) by wires (804) from the edges.Electrical-conducting/thermal-insulating (ECTI) materials may need to behigh electrical conductors and poor heat conductors. Traditionalelectrical conductive composites are often highly heat conductive aswell.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system as an ECTI material. Preferably, a threecomponent system can be used, with component A being at least one ofthermoset, thermoplastic, or rubber polymer, with component B being alow melting point polymer or low molecule weight compound, and withcomponent C being an electrically conductive filler that selectivelyenters into component B. Even more preferably, four component system canbe used, with component A being at least one of thermoset,thermoplastic, or rubber polymer, with component B being a low meltingpoint polymer or low molecular weight oligomer, with component C beingthe electrically conductive filler that selectively enters intocomponent B, and with component D being a low thermal conductive fillerthat preferentially enters into component A. Even more preferably, thecomponent D can be a nano sized spherical low thermal conductive fillerto maximize the phonon reflecting interface. More preferably, the matrixcan be a block co-polymer, which forms electrically conductive channelscontaining electrically conductive filler (component C) along thedesired heat conducting direction.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one matrix material thatis one of thermoplastic, thermoset or rubber material, for use as anECTI material. More preferably, the matrix material is capable ofproviding mechanical properties and physical properties based on theapplication requirements. Examples of matrix materials include, but arenot limited to, silicone rubber, epoxy resin, phenolic resin, polyimide,unsaturated polyester, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one second phase polymermaterial, for use as an ECTI material. More preferably, the second phasepolymer is immiscible with the matrix material. Examples of second phasepolymers include, but are not limited to, polyethylene oxide for epoxyresin matrix, poly(E-carprolactone) for silicon rubber, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one block copolymermatrix material, for use as an ECTI material. More preferably, thematrix can be a block copolymer with one block being the low meltingpoint polymer. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),Poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with lowaspect ratio, for use as an ECTI material. Preferably, the fillers enterinto the second phase material. More preferably, fillers with highelectrical conductivity can be used. Examples of fillers include, butare not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy,Gd, etc. Even more preferably, nanoparticles can be used. Example ofnanoparticles include, but are not limited to, carbon blacknanoparticles, C60 fullerene, gold nanoparticles, silver nanoparticles,etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with highaspect ratio, for use as an ECTI material. Preferably, the fillers enterinto the second phase material. More preferably, fillers with highelectrical conductivity can be used. Examples of fillers include, butare not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy,Gd, etc. Even more preferably, nanowires and nanorods can be used.Examples include, but are not limited to carbon nanotubes, silvernanowires, gold nanorods, etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system comprising electrically conductivefillers confined in low melting point second polymer phase and anothertype of fillers in the matrix polymer. Preferably, the fillers in thematrix material have low thermal conductivity. Examples of low thermalconductive fillers include, but are not limited to, SiO₂, Al₂SiO₅,Al₂O₃, etc. Even more preferably, the fillers can be well dispersednanowires, nanoparticles, nanoflakes, and nanorods to maximize thephonon scattering interface. Examples includes but are not limited to,glass fibers, SiO₂ nanoparticles, Al₂SiO₅ nanoflakes, etc.

Example Non-Limiting Application as Underfill Materials

FIG. 9 shows an exemplary underfill material (901) applied on to an ICcircuit board substrate (902). The IC chip (903) is placed on top of thesolder balls (904). Pressure is applied on the IC chip so that thesolder balls deform at elevated operating temperature to form electricalconnection between IC chip and IC circuit board substrate. The underfillmaterial is squeezed out slightly and form a wrap around the IC chip.Finally, the underfill material solidifies to immobilize the IC chip.Traditional underfill materials are mostly micro-sized thermalconductive particle filled or unfilled adhesive polymers. Heatdissipation in the underfill is one of the major issues for ICpackaging. Microsized particle filled underfill materials often sufferfrom inhomogeneous filler segregation and poor processability as aresult of high viscosity.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system as an underfill material. Preferably, a threecomponent system can be used, with component A being at least one ofthermoset, thermoplastic, or rubber polymer, with component B being alow melting point polymer or low molecule weight compound, and withcomponent C being an electrically conductive filler that selectivelyenters into component B. More preferably, four component system can beused, with component A being at least one of thermoset, thermoplastic,or rubber polymer, with component B being a low melting point polymer orlow molecular weight oligomer, with component C being the electricallyconductive filler that selectively enters into component B, and withcomponent D being a low thermal conductive filler that preferentiallyenters into component A. The component D can be a nano sized sphericallow thermal conductive filler to maximize the phonon reflectinginterface. The matrix can be a block co-polymer, which formselectrically conductive channels containing electrically conductivefiller (component C) along the desired heat conducting direction.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one matrix material thatis one of thermoplastic, thermoset or rubber material, for use as anunderfill material. More preferably, the matrix material is capable ofproviding mechanical properties and physical properties based on theapplication requirements. Examples of matrix materials include, but arenot limited to, silicone rubber, epoxy resin, phenolic resin, polyimide,unsaturated polyester, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one second phase polymermaterial, for use as an underfill material. More preferably, the secondphase polymer is immiscible with the matrix material. Examples of secondphase polymers include, but are not limited to, polyethylene oxide forepoxy resin matrix, poly(ε-carprolactonc) for silicon rubber, etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one block copolymermatrix material, for use as an underfill material. More preferably, thematrix can be a block copolymer with one block being the low meltingpoint polymer. Examples include, but are not limited to,polydimethylsiloxane-b-ethylene oxide (PDMS-b-PEO),Poly(dimethylsiloxane-b-ε-caprolactone) (PDMS-b-PCL),poly(urethane-b-dimethylsiloxane).

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with lowaspect ratio, for use as an underfill material. Preferably, the fillersenter into the second phase material. More preferably, fillers with highelectrical conductivity can be used. Examples of fillers include, butare not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy,Gd, etc. Even more preferably, nanoparticles can be used. Example ofnanoparticles include, but are not limited to, carbon blacknanoparticles, C60 fullerene, gold nanoparticles, silver nanoparticles,etc.

One exemplary non-limiting illustrative embodiment provides a multiplecomponent composite system comprising at least one filler with highaspect ratio, for use as an underfill material. Preferably, the fillersenter into the second phase material. More preferably, fillers with highelectrical conductivity can be used. Examples of fillers include, butare not limited to, C, Ag, Au, Cu, Ni, Pt, Pd, Fe, Pb, Al, Zn, Co, Dy,Gd, etc. Nanowires and nanorods can be used. Examples include, but arenot limited to carbon nanotubes, silver nanowires, gold nanorods, etc.

One exemplary non-limiting illustrative embodiment provides amulti-component composite system comprising electrically conductivefillers confined in low melting point second polymer phase and anothertype of fillers in the matrix polymer. Preferably, the fillers in thematrix material have low thermal conductivity. Examples of low thermalconductive fillers include, but are not limited to, SiO₂, Al₂SiO₅,Al₂O₃, etc. More preferably, the fillers can be well dispersednanowires, nanoparticles, nanoflakes, and nanorods to maximize thephonon scattering interface. Examples includes but are not limited to,glass fibers, SiO₂ nanoparticles, Al₂SiO₅ nanoflakes, etc.

While the technology herein has been described in connection withexemplary illustrative non-limiting implementations, the invention isnot to be limited by the disclosure. The invention is intended to bedefined by the claims and cover all corresponding and equivalentarrangements whether or not specifically disclosed herein.

We claim:
 1. A process for assembling a system having enhanced thermalconductivity, comprising: Providing an integrated circuit and a heatsink; and Forming a multi-component thermal conductor therebetween,wherein the multi-component thermal conductor comprises a matrixmaterial with a second phase material comprising filler materialdispersed therein.
 2. A transparent multi-component electricalconductor, comprising: a first component comprising a opticallytransparent matrix polymer; a second component comprising an opticallytransparent, low melting point material immiscible with the firstcomponent; and a third component comprising a filler material withhigher electrical conductivity than the first and second components;wherein the third component is dispersed into the second component andthe second component is dispersed within the polymer matrix and whereinthe third component provides enhanced electrical conductivity to themulti-component electrical conductor.
 3. The optically transparentmulti-component electrical conductor, according to claim 2 wherein thefirst and second component each have an index of refraction that areclose enough to each other to avoid significant optical scattering. 4.The optically transparent multi-component electrical conductor accordingto claim 2, wherein the first, second and third components each have anindex of refraction and wherein the real part of the indices ofrefraction of the first, second and third components are close enough toeach other to avoid significant optical scattering.
 5. A method ofinducing alignment of high aspect ratio filler along the heat and/orelectricity conduction direction comprising: applying an externalelectric and/or magnetic field, and self aligning due to geometricconfinement of fillers in the second phase material at least in part inresponse to said field.